Lubricating oil blend



iatented Mar. 21, 1944 2,344,912 LUBRICATING on. BLEND David W. Young, Roselle, and Hector C. Evans,

Crani'ord, N. 1., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application April 15, 1942, Serial No. 439,082

8 Claims. (Cl. 252-59) This invention relates to hydrocarbon lubricating oil blends with additives that eflect improvement in viscosity characteristics. More particularly, it relates to novel additives characterized by highly aromatic type polymers of tri-arylmethyl radicals.

An object of this invention is to provide lubricating oil compositions of enhanced viscosit index characteristics.

Another object is to provide homogeneous lubricating oil blends with a viscosity index improver which is highly efiective in parafllnic oils and proper mixtures of parafllnic oils with naphthenic type or lower viscosity index oils.

A further object 01' this invention is to provide oil blends with a viscosity index improving additive that has a distinctively high stability against mechanical breakdown.

Other objects and advantages will appear from the following description.

Unlike polymers of oleflnic substances which have thus far been found most practical as viscosity index improvers, highly aromatic type polymers of the present invention have a relatively low solubility in paraflinic petroleum lubricating oils. They have a greater resistance to mechanical breakdown. Also they exhibit better ability to improve the viscosity index of lubricating oils with less thickening.

In a specific embodiment of this invention it was found that polymer products resulting from disproportionation of tri-arylmethyl radicals are usefulblending agents or additives for accomplishing the object set forth. While there is still more to be learned about the structure and composition of these polymers, investigations have indicated that they contain a quinoid type unit which is unsaturated and thus readily absorbs oxygen or similar reactive substances. Basically, these polymers are formed by the coupling of free tri-arylmethyl radicals which might be derived by several types of reactions, such as (1) dissociation of hexa-aryl ethanes, (2) disproportionation of tri-arylmethane resulting from the removal of hydrogen from a free tri-arylmethyl radical, and (3) by electrolysis of aromatic Grignard reagents.

The trl-arylmethyl molecules which give the desired polymerization products have been represented as having the following type 01 structure:

This structure is subject to variation with respect to the alkyl substituents in the aryl groups as, for example, some of the aryl groups may be phenyl radicals, or some of the aryl groups may contain higher alkyl substituents, but so far it has been found preferable to have in the unit a para-methyl-phenyl or tolyl group.

In studying the properties of these polymers,

'nxAMPLE 1 The polymer tested as a petroleum lubricating oil additive was the polymeric product derived from the disproportionation of tri-p-tolylmethyl. This polymeric material consisted of a brownish-yellow powder which was fairly soluble in hexane, in benzene, and in tetrahydronaphthalene but almost insoluble in ether. Descriptions of methods for preparing these polymers are given in the Journal of the American Chemical Society, vol.

61; October 1939, pages 2769 to 2775; vol. 63, September 1941, pages 2316 to 2320; and October 1941, pages 2574 to 2576. In accordance with these articles, a convenient method of preparation consists in heating tri-p-tolylmethyl chloride under reflux conditions with dry pyridine in an-atmosphere of nitrogen. Under these conditions, the chloride is considered to be decomposed to the free tri-p-tolylmethyl radical. which in turn undergoesa rearrangement known as disproportionatior to yield tri-p-tolylmethane and the free radical having a high degree of unsaturation which may assumea quinoid structure that finally results in a;polvmeric residue.

The polymer thus obtained was used to formulate blends with a naphthenic mineral lubricating oil having a V. I. of 65.8 and with a paramnic lubricating oil having an original V. I. of 110.8. The elects oi the added polymer on the viscosity characteristics of these oils are shown in the The results shown in the foregoing table demonstrated that the tri-arylmethyl polymer has exceptionally high if. I, improving potency combined with a desirably restricted thickening action as compared to polymerized oleflns which have considerably higher solubility in parammc petroleum oils. For example, a comparison may be made with a representative isobutylene polymer thickener blend with the same type oi paraffinic base oil. The efiects of this thickener are shown in the following table:

TABLE II 4 Saybolt seconds I Pgl'cfil? iso- Universsl visi- Base lubricating oil v. I.

added None 158. 2 44. 37 110. 8 O. 6 197. 4 48.98 128. 1 D 1.2 248.0 54.18 1.32.2

By comparing the efiects of the two types of polymer in the parafin base lubricating oil, it can be seen that the tri-p-tolylmethyl polymenraises the viscosity of the oil at 100 F. onlyby about 10% in giving substantially the same if. 1. improvement as obtained in thickening the same base oil with the isobutylene polymer at 100 F. to the considerably greater degree of more than Thus, the highly aromatic polymer is much more effective for increasing the V. I. of the paraflinic oils with restricted thickening, which is an important factor in maintaining the grade of the lubricating oil. I

Breakdown tests on the highly aromatic polymer very clearly demonstrated its high resistance to mechanical breakdown as is shown in the following results obtained when the parafiin base oil containing 1% of the tri-tolylmethyl polymer was forced through the capillary tube 4.55 cm. in length and 0.0109 cm. in radius. After each passage through the capillary tube, the viscosity characteristics of the polymer blend were determined and these showed no appreciable change in the viscosities and therefore no appreciable breakdown of the polymer.

Gil

Tsnu: III a Pressure viscoaimeter breakdown test Pressure -lbs./sq. 1a- 1440 Rate or now. 'g./minute 17.2 Temperature FL- 92 Bayboit seconds v Univ.viscosity Pass number f In contrast to the above results, in general, the linear aliphatic polymer V. I. improvers with molecular weights above 10,000 undergo a substantial breakdown in the initial passes through the pressure viscosimeter capillary tube at 92 F.

as is exhibited by substantial decreases in the viscosities of the oil blends containing them.

As already mentioned, the described highly aromatic polymers contain a certain amount of unsaturation which makes them readily add on oxygen, .but in place of oxygen, other substances which react with double bonds may be incorporated into the polymers as, for example, hydrogen. halogens, sulfur, or similar metalloids, organic groups, or metal-containing groups.

One may take fuller advantage of the high V. I. improving efiectiveness of these highly aromatic polymers and their restricted solubility in parafiinic oils by using the polymers in a ternary lubricating composition in which the polymers are homogeneously blended with a naphthenic or aromatic oil and with a highly paraflinic oil as an anti-solvent to obtain optimum polymer s01- ubility and superior V. I. immoving properties. In such ternary compositions. the highly naphthenic or aromatic oil may havea relatively low viscosity as compared to the paraiiinic oil. Such compositions are indicated to be very satisfactory in their low pour points, high V. 1., and high stability properties for use as hydraulic fluids.

The following examples are given to demonstrate the viscosiiy producing property of an aromatic type polymer in a ternary lubricating composition: 2

copolymer was dissolved in 99 gramsof the 6.5 I

V. I. oil at about F. and viscosity results on the resulting blend are listed:

TABLE IV 'lempera- Viscosity in Age of ture centlstokes solution 1 F. Hours 60 250. l 29 68 196. 3 29 100 60. 76 29 150 17. 45 29 210 6. 63 29 Calculated A. s. T. M. slope over 00 F. to 210 12-0105.

To the polymer solution with a viscosity of 6.63 centistokes at 210 R, by weight of the 112.9 V. I. parailinic mineral oil was added. After the ternary mixture had been agitated at room temperature, the viscosity of the product was determined and the checked results are listed:

Tarts V pprox. Approx. Temper- Viscosit in Viscosit in se of stun centllto es solution centisto es solution T. V Hours Hours 60 100. l 18 198. 7 177 68 168. 7 18 108. 8 177 100 54. 6 18 64. 7 177 13) 24. 7 18 24. 7 l77 150 16. 2 l8 l6. 3 177 210 6. 3 l8 6. 3 177 Calculated A. 8. T. M. slope over (I? F. to 210 F. -0.775

log =m log 1+1lz log or where =viscosity m=mol. fraction of solution 1 m=mol. fraction of solution 2 EXAMPLE3 To the 1% copolymer-oil blend (that had a viscosity at 210 1''. of 6.63 centistokes and an A. S. T. M. slope of .795 over the temperature range of 60 F. to 210 F.) were added 40% by weight of the polymer non-solvent oil that had a v. I. of 112.9. viscosity results on the resulting solution are listed:

Tun: VI

Tempera- Visoosi in Age of Visoosit in Age of turs centisto solution centisto es solution '5'. Hum Hour; 68 136. 02 8 136. 06 227 100 50. 69 8 50. 71 227 150 15. 77 8 l5. 7! 227 210 5. 87 8 5. 8B 277 Calculated A. S. T. M. slope over 68 F. to 210 F.-0.796.

These data indicate that the ternary lubrication mixture has a determined Ubbelohde viscosity at 68 F. that is calculated to be about centistokes lower than would be expected from plotted data obtained on the same chart as used in Example 1. The calculated theoretical A. S. T. M. slope for this oil over the temperature range of 68 1'". to 210 F. is 0.814.

The results in Examples 2 and 3 indicate that normal blending laws do not hold for these ternary solutions at temperatures below about 70 1''. These data also indicate that as the temperature is raised, a larger amount of non-solvent oil is used to obtain the desired reduction in viscosity'at the lower temperature. For example, in the temperature range of 60 F. to 210 F., 10% non-solvent oil decreased the A. S. T. M. slope by 0.020, but over the temperature range of 68 F. to 210 F. it required 40% non-solvent oil to decrease the A. S. T. M. slope by 0.018.

Gen'erically, the highly aromatic polymers that act appropriately in the described ternary blends are P lymers which have a low solubility in parafllnic petroleum lubricating oils and relatively higher solubility in naphthenic or nonparamnic petroleum lubricating oils. They may have molecular weights ranging from about 5,000 to 25,000. From the nature of their syntheses, they contain a substantially larger number of carbon atoms in aromatic ring than in aliphatic chain structures,but nevertheless, preferably contain alkyl group branches. The aromatic polymers which have given particularly good results contained from about 2 to 6 carbon atoms in aromatic rings for each 1 carbon atom in aliphatic (alkyl or alkylene) group.

A scheme found useful for determining how variations in aromaticity of the polymers affects the behavior as viscosity index improving agents is illustrated in studies of copolymers prepared from styrene and isoprene. By these studies it was found that with increase of the aromaticity of the polymers by increasing the proportion of the aromatic reactant, styrene, so as to lower the solubility of the polymers in parafl'inic oils, the polymers were made more eflective as viscosity index improvers so long as they still could be dissolved in naphthenic or non-parailinic oils.

This is shown by the following data:

TABLI VII Polymer con- Pol er constituents W centration m ml V. I. Percent Percent oil who homo 1'. 210 F.

None 234.6 44.1 6.6 I. 0 64 36 282. a 5. 6 25. 6 l. 0 66 34 200. 1 7. 3 33- 3 l. 0 68 33 287. 2 47. 4 a. 0 l. 0 70 30 280. 7 47. 9 46. 3

The improved oil blends prepared in accordance with this invention may contain two or more types of viscosity index improvers. They may also contain other kinds of oil additives useful for stabilizing, dyeing, inhibiting oxidation, imparting oiliness, lowering the pour point, reducing sludging, or imparting extreme pressure properties, etc.

The present invention has been illustrated by typical examples but is not intended to be limited thereby nor is it intended to be limited by any theory on the mechanism by which the improvement is obtained, nor to any particular kind of hydrocarbon oil, specific polymer composition, or blend. Any modification coming within the spirit of the invention is intended to be included within the scope thereof as defined in the following claims.

We claim:

1. A lubricating composition comprising a highly aromatic polymer containing from about 2 to 6 carbon atoms in aromatic rings for each carbon atom in aliphatic group which has a low solubility in a parailln base lubricating oil.

dissolved in a non-parailinic oil in a concentration.above its solubility in a paraiilnic oil, and said solution being homogeneously blended with a paraflinic oil restricted in amount to avoid precipitation oi the polymer.

2. A ternary lubricating composition which consists in a homogeneous solution of a highly aromatic polymer containing from about 2 to 6 carbon atoms in aromatic rings for each carbon atom in an aliphatic group in a non-paraflinic hydrocarbon oil to which said polymer imparts an improved viscosity index, and a parafllnic mineral lubricating oil which is less miscible with said polymer in an amount that prevents precipitation of the polymer but increases the viscoflty index improving eilectiveness of merelymer. 4

16 petroleum lubricating oil base blended with a small amount of a tri-p-tolylmethyl polymer.

I DAVID W. YOUNG.

HECTOR C. EVANS. 

